![Page 1: Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004 High Level Trigger for the ttH channel in fully hadronic decay at LHC with the CMS detector](https://reader030.vdocument.in/reader030/viewer/2022032704/56649d4d5503460f94a2b931/html5/thumbnails/1.jpg)
Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
High Level Trigger for the ttH channel in fully
hadronic decay at LHC with the CMS detector
Daniele Benedetti
On behalf of CMS Collaboration
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
OutlookReason for studying ttH channel
Study of the data acquisition
• Current Higgs mass limits
• The role of the LHC collider
• CMS data acquisition system
• The Level 1 Trigger
• The High Level Trigger (HLT) ttH in fully
hadronic decay
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
Large Hadron Collider (LHC)
Circumference: 27 KmEnergy CM (p-p)=14 TeV
Hadronic Calorimeter
Electromagnetic Calorimeter
Tracker
Chambers
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
Higgs mass previsionFrom Lep measures Higgs mass > 114.1 GeV at 95% C.L.
With the new world average for:
MH<251 GeV (2 ) 95% C.L.
Mtop = (178.0 ± 4.3) GeV
And the best estimate for Higgs mass is:
MH=117 GeV
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
Interactions at LHC
s [TeV]
H(mH=500 GeV)10-7
10-5
10-3
10-1
101
103
105
107
109
10-6
10-4
10-2
100
102
104
106
108
1010
tot
b
jet(ETjet>s/20)
W
Z
jet(ETjet>100 GeV)
t
jet(ETjet>s/4)
H(mH=120 GeV)
TeVatron LHC
[n
b]
R@
L=10
34 c
m-2s-1
[H
z]
.1 1 10
Production of quarks b
Production of quarks top
Production ofHiggs
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
Higgs observabilityFor MH (120-130) GeV
Cross Section
BranchingRatio
ExpectedBackgroun
d
Observability
ggHbb P1+D1
No
ggH P1+D2
Yes
ggttHttbb P2+D1
?
P1
D2
D1
P2
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
The Channel ttH Fully hadronic final state
8 (or more) jets in the final state and 4 from quark b
quarkHadronization
jets
MH=120 GeV
Branching Ratio
W qq 67.6%H (120 GeV) bb 71.3%Total hadronic 32.6% (pb)
ttH (LO) 0.5773ttH(NLO) 0.7015ttH hadronic (LO) 0.1881ttH hadronic (NLO) 0.2286
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
Background considered
Cross Section (mb)Exepected rate at lowLuminosity (2x1033 cm-
2s-1)
QCD(30<pT<50 GeV)
0.195770 ~4x105
QCD(50<pT<80 GeV)
0.025870 ~ 5x104
QCD(80<pT<120 GeV)
0.003629 ~ 7.3x103
QCD(120<pT<170 GeV)
0.000619 ~ 1.2x103
For the trigger study we used non resonant background. The QCD samples are datasets of the official CMS Production 2002
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
CMS Trigger
105 events/s (Hz)
Use of chamber and calorimeters
100 Hz
Also using tracker
Interaction p-p: 40 MHz
Total reduction factor >105
L1
HLT
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
Eff ttH Rate QCD4 ET > 40 GeV
80 % 1 KHz
4 ET > 50 GeV
65 % ~200 Hz
Rate(s-1)=eff x (mb) x 1027x L(cm-2 s-1)Luminosity=2x1033 cm-2 s-
1
p pT ET
Trigger L1 ttH hadronic
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
Fast b-tagging for HLT
jetvs
vpd0
d0
• Regional Tracking
•Conditional Tracking
Only tracks within a jet cone R=0.4
R2= (jettracks)2+(jettracks)2
(jet, jet) from L1 jet reconstruction
Limited number of hits
Pt tracks in pixel line > 2 Gev/c
do resolution
pt resolution
do = impact parameter
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
High Level Trigger We use the Tracker information to recognise the jets from quark b
Partial reconstruction 5 hits track reco 0.4 cone 2 GeV pxl line Pt cut
Requiring SIP 2D > 2 We reject more QCDthan signal
SIP2D = Significance of impact parameter in 2D
Sip2D
track
s
Black = ttH hadronic Red = QCD
Sip2D= d0
d0
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
High Level Trigger
The b-tagging is a track counting algorithm:2 tracks at different SIP2D
For 1 b-tagging jet0.5 < Sip2D < 5For 2,3,4 b-tagging jet0.5 < Sip2D <2.5
2 tracks with Sip2D>2.0:
85% sig eff25% QCD eff
Preselection ET>10 GeV
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
2 tracks with Sip2D>2.0:
30 Hz QCD Rate with 60 % Eff
High Level Trigger (100 Hz)
• 4 jets with ET>50 GeV• 1,2,3,4 b-tagged jet
Requiring:
Energy Trigger + b-tagging
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Daniele Benedetti CMS and University of Perugia Chicago 07/02/2004
Conclusions• With the L1 Trigger (4 jets with ET>50 GeV) we obtain65% signal efficiency at ~200 Hz of QCD rate.
• With the High Level Trigger we can decrease the QCD rate to 30 Hz still selecting 60% of signal events.
…next steps
Study the offline reconstruction and estimate the signal significance with respect to the resonant backgrounds.